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Investors were concerned after Apple(NASDAQ:AAPL) reported slower-than-expected unit shipment growth for its iPhone business in the company's first fiscal quarter of 2014. The market's worries have merit; not only is Apple's iPhone business its most profitable business, but it also accounts for more than half of the tech giant's total revenue. Fortunately for Apple shareholders, however, Apple's slowing iPhone sales growth may soon begin to tick upward again (or at least stabilize) when the company launches its iPhone 6 models later this year. A new survey from ChangeWave (via Fortune) suggests pent-up demand for the rumored larger phone may exceed the demand prior to the iPhone 5 and the 5s launches.

Consumer excitement for a larger iPhone While details regarding Apple's upcoming iPhone 6 models still remain shady, most speculation seems to agree on one point: The iPhone 6 models will likely sport displays larger than the 4-inch display used in the iPhone 5 and 5s.

While competitors capitalize on consumer demand for larger displays, Apple has yet to even make one phone with a display larger than 4 inches. Samsung, Apple's most formidable smartphone competitor, has done an excellent job on capitalizing on demand for larger displays, with its Galaxy S5 (measuring 5.1 inches) as the latest model to join its lineup up of larger smartphones.

Though Apple may have missed out on incremental upside from this fast-growing market in the past few years, the consumer suspense has built up considerable demand for Apple's alleged larger iPhone 6 models. A March survey of 4,109 U.S.-based ChangeWave members showed that 26% were "somewhat likely" to purchase an iPhone 6 with a larger screen size and a subsidized price point of $199. Fourteen percent were "very likely" to buy it. These results trump the demand displayed ahead of the iPhone 5 and 5s launches. For the iPhone 5s, 17% and 9% of members were somewhat and very likely to buy the device, respectively. For the iPhone 5 those figures were 18% and 15%.

ChangeWave Research, a service of 451 Research, concluded:

"This is the highest level of demand for an unannounced Apple model in a ChangeWave survey -- stronger than we've seen in previous years for the iPhone 5S and iPhone 5 models prior to their announcements," said Andy Golub of 451 Research. "Speculation over a larger screen iPhone is clearly striking a chord with consumers."

Putting the icing on the cake for Apple's opportunity, ChangeWave also says that interest in phablet devices, or large smartphones, has recently climbed to an all-time high among its members.

The described iPhone 6 in the ChangeWave survey was similar to the rumored specs on Apple's upcoming iPhone models. The latest buzz hints at two different display sizes for the iPhone 6, a 4.7-inch and a 5.5-inch model. Well-connected KGI Securities analyst Ming Chi Kuo predicts Apple to launch the 4.7-inch model this fall and the larger model toward the end of the year.

A reason to buy Apple stock?With gross profit margins seeming to stabilize at impressive levels and Apple's top line still growing, the company's conservative valuation is already questionable given Apple's current business performance. But once you add in the rumors for Apple's larger iPhone 6 that ChangeWave seems to believe will be welcomed in the market place by meaningful pent-up demand, Apple stock may be offering investors an excellent entry points at today's price.